mysql子查询返回多列

SELECT 
    c.customer_id, 
    c.customer_name, 
    (SELECT COUNT(*) FROM orders o WHERE o.customer_id = c.customer_id) AS order_count,
    (SELECT SUM(o.amount) FROM orders o WHERE o.customer_id = c.customer_id) AS total_amount
FROM 
    customers c;

SELECT 
    c.customer_id, 
    c.customer_name, 
    COUNT(o.order_id) AS order_count,
    SUM(o.amount) AS total_amount
FROM 
    customers c
LEFT JOIN 
    orders o ON c.customer_id = o.customer_id
GROUP BY 
    c.customer_id, c.customer_name;